1. Field of the Invention
The present invention relates to a clutch apparatus having a clutch outer member linked and coupled to an input member, a clutch inner member linked and coupled to an outer member, a plurality of drive friction plates engaging the clutch outer member, a plurality of driven friction plates interleaved with the drive friction plates and engaging the clutch inner member, a pressure bearing plate disposed in confronting relation to one of the drive friction plates and the driven friction plates that is disposed at an end along an axial direction of the clutch inner member, a presser plate sandwiching the drive friction plates and the driven friction plates between itself and the pressure bearing plate, clutch springs for exerting a biasing force to bias the presser plate to compress the drive friction plates and the driven friction plates between the presser plate and the pressure bearing plate, and a compressive force boosting means for boosting the biasing force applied from the clutch springs to the presser plate in response to accelerated rotation of the clutch inner member.
A plurality of first clutch springs can be disposed between a first spring retainer immovable relatively to the pressure bearing plate in the axial direction and the presser plate, for biasing the presser plate to compress the drive friction plates and the driven friction plates between the presser plate and the pressure bearing plate. In addition, a plurality of second clutch springs can be disposed between a second spring retainer movable relatively to the pressure bearing plate in the axial direction and nonrotatable relatively to the presser plate and the presser plate, for biasing the presser plate to compress the drive friction plates and the driven friction plates between the presser plate and the pressure bearing plate. A compressive force boosting means can be provided having a cam mechanism disposed between the clutch inner member and the output shaft and having a movable cam member as one of components thereof, for actuating the second spring retainer to boost biasing forces of the second clutch springs depending on movement of the movable cam member in response to accelerated rotation of the clutch inner member.
A back torque limiter means is provided for moving the presser plate away from the pressure bearing plate when a drive force from the output member is greater than a drive force from the input member.
2. Description of Background Art
Japanese Patent Laid-Open No. 2011-190885 discloses a known clutch apparatus having clutch springs disposed between a spring retainer and a presser plate that are mounted on a clutch inner member, such that the springs exert biasing forces to bias the presser plate into a compressed state, and compressive force boosting means that boosts the biasing force applied by the clutch springs to the presser plate in response to accelerated rotation of the clutch inner member by moving the clutch inner member such that the spring retainer moves toward the presser plate. The compressive force boosting means includes a fixed cam member and a movable cam member that have oblique teeth held in mesh with each other. It is difficult for the movable cam to be integrally formed with the clutch inner member to be driven in view of the rigidity and machinability of the meshing teeth. According to Japanese Patent Laid-Open No. 2011-190885, the movable cam member that is separate from the clutch inner member is fixed to the clutch inner member by rivets.
The structure disclosed in Japanese Patent Laid-Open No. 2011-190885 wherein the separate movable cam member is fixed to the clutch inner member needs fasteners such as rivets or the like. Thus, the structure is made up of an increased number of parts.
According to Japanese Patent Laid-Open No. 2011-190885, a clutch apparatus may have a plurality of first clutch springs disposed between a first spring retainer immovable relatively to a pressure bearing plate in an axial direction of a clutch inner member and a presser plate. A plurality of second clutch springs are disposed between a second spring retainer movable relatively to the pressure bearing plate in the axial direction and nonrotatable relatively to the presser plate and the presser plate. A compressive force boosting means has a movable cam member for actuating the second spring retainer to boost biasing forces of the second clutch springs in response to accelerated rotation of the clutch inner member.
The compressive force boosting means partly includes a fixed cam member and a movable cam member that have oblique teeth held in mesh with each other. Upon accelerated rotation of the clutch inner member, the movable cam member angularly moves relatively to the fixed cam member and also moves axially. According to the clutch apparatus disclosed in Japanese Patent Laid-Open No. 2011-190885, the pressure bearing plate and the fixed cam member are relatively nonrotatably coupled to the output shaft, and the movable cam member is fixed to the clutch inner member. A plurality of first bosses which extend through the presser plate have respective ends fixed to the pressure bearing plate, and the first spring retainer is mounted on the respective other ends of the first bosses. A plurality of second bosses which extend through the presser plate have respective ends fixed to the movable cam member, and the second spring retainer is mounted on the respective other ends of the second bosses. In order to prevent the first bosses and the presser plate from interfering with each other when the movable cam member is angularly moved relatively to the fixed cam member, insertion holes defined in the presser plate for the insertion of the first bosses therethrough have to be oblong in shape. The number of man-hours required to machine the presser plate is greater than if the insertion holes are circular in shape, and washers are needed to avoid adverse effects caused by frictional contact between the presser plate and the first clutch springs which bear shearing forces, resulting in an increase in the cost of the clutch apparatus.
In addition, according to Japanese Patent Laid-Open No. 2011-190885, there is known a clutch apparatus having clutch springs disposed between spring retainers on a clutch inner member and a presser plate for exerting biasing forces for biasing the presser plate into a compressed state. A back torque limiter means is provided for moving the presser plate away from a pressure bearing plate against the biasing forces from the clutch springs when a drive force from an output member is greater than a drive force from an input member. The back torque limiter means presses the clutch inner member with the presser plate to which a movable cam member serving as part of a cam mechanism is fixed.
With the structure disclosed in Japanese Patent Laid-Open No. 2011-190885 wherein the presser plate is pressed by the clutch inner member, the clutch inner member is a relatively large component and has a large inertial mass. Therefore, when a back torque is generated, since the movable cam member and the clutch inner member coupled to the movable cam member are moved by forces generated by a cam action of the cam mechanism, the timing of applying a pressing force from the clutch inner member to the presser plate possibly tends to be delayed. Thus, it is desirable to increase the response of the back torque limiter means when a back torque is generated.